This invention concerns the production and recovery of methyl tert. butyl ether, a valuable compound which can be used, for example, as high octane rating gasoline component.
It is well known to react isobutene with methanol in the presence of acid catalysts to obtain methyl tert. butyl ether (MtBE), as disclosed, for example, in the U.S. Pat. Nos. 2,480,940 and 3,037,052.
Isobutene is commonly used as a C.sub.4 cut which comprises, in addition to isobutene, other mono-olefins and saturated hydrocarbons, and possibly small amounts of acetylenic or diolefinic hydrocarbons. This cut may be obtained, for example, by steam-cracking, catalytic cracking or dehydrogenation of hydrocarbons. Its isobutene content ranges, for example, from 5 to 70% by weight or more.
The reaction product of this balanced reaction normally contains, in addition to MtBE, unconverted methanol and isobutene, as well as the other hydrocarbons of the C.sub.4 cut. The use of a methanol excess, to displace the reaction balance, increases the isobutene conversion rate, although the latter conversion is never complete.
The problem of fractionating this mixture by distillation is not simple, since azeotropes form, whose composition is unfavorable: a methanol/MtBE azeotrope and C.sub.4 hydrocarbons/methanol azeotropes. The known attempts to fractionate this mixture rely on relatively complex and expensive operations, combining distillations, washings, recyclings, etc.